HR: 1330h
AN: S42C-0186    [PDF]
TI: EXAMINING MECHANISM DEPENDENT SEISMIC RADIATION IN 3D SPONTANEOUS RUPTURE MODELS
AU: Ma, S
EM: sma@crustal.ucsb.edu
AF: Institute for Crustal Studies, University of California, Santa Barbara, Santa Barbara, CA 93106 United States
AU: * Archuleta, R
EM: ralph@crustal.ucsb.edu
AF: Institute for Crustal Studies, University of California, Santa Barbara, Santa Barbara, CA 93106 United States
AB: The mechanism-dependence of radiated seismic energy generated by earthquakes is investigated by modeling dynamic ruptures for three different fault mechanisms in three dimensions: a 30$\deg$ dipping reverse fault, a 60$\deg$ dipping normal fault and a vertical strike-slip fault. All three faults have the same area and are subjected to the same stress conditions in a homogeneous half-space. Except for the geometry and the mechanism, all other conditions are identical. Following the work of Favreau and Archuleta (2003) both the work distribution on the fault and the work done by seismic waves against distant surfaces enclosing the source for the three different mechanisms are calculated using a 3D finite element method. In a recent study Perez-Campos and Beroza (2001) examined the far field energy radiation from previous earthquakes. Even though there is a large scatter in the results, they found that the radiated seismic energy is strongly mechanism-dependent: the average apparent stress for strike-slip earthquakes is ~4.8 times higher than for reverse events and ~1.8 times higher than for normal events (0.7 MPa for strike-slip events and 0.15 and 0.25 MPa for thrust and normal faults, respectively). These results are opposite to what is expected for the state of stress. In 2D dynamic simulations (Ma and Archuleta, 2002) we show that the three faults have almost the same seismic moment and radiate nearly the same amount of seismic energy for strike-slip and normal with a 50 percent increase for thrust. The apparent stress is 0.45 MPa, 0.29 MPa and 0.31 MPa for the reverse fault, normal fault and strike-slip fault, respectively. By looking at the energy distribution on a surface surrounding the fault we found most energy is confined near the free surface, i.e., most radiated energy propagates out as surface waves. The energy associated with small takeoff angles, i.e., energy that goes to teleseismic distance, is very small. We are doing simulations in three dimensions to investigate the mechanism-dependent radiated energy in a more realistic environment and to check possible 3D effects on our previous results.
DE: 7200 SEISMOLOGY
DE: 7209 Earthquake dynamics and mechanics
DE: 7223 Seismic hazard assessment and prediction
DE: 7843 Numerical simulation studies
DE: 8010 Fractures and faults
SC: Seismology [S]
MN: 2003 Fall Meeting